Other atomization methods which are conventionally known include 1) single fluid hydraulic spray nozzles and 2) two-fluid injection nozzles. Single fluid hydraulic spray nozzles pressurize a liquid without using gas, so that the liquid is sprayed out through small-diameter injection openings after passing through a revolving (spiral) passageway. Two-fluid injection nozzles atomize a liquid at the injection openings by using a high-speed gas to blow about and break up the liquid.
In both cases, however, the diameter of the sprayed particles is about 0.1 mm, with neither method being applicable when a smaller particle spray is desired. Moreover, in the case of the former nozzle, shearing stress on the high-pressure liquid results inside the nozzle, while the latter nozzle involves a process in which the liquid is broken up a number of times using the high speed gas. Accordingly, when the liquid contains vital cells, or pressure-sensitive components or structures, neither of the above-described methods can be used due to the considerable damage they cause.
In recent years, 3) ultrasonic wave nozzles have been developed. However, since the travel distance of the spray depends solely on the momentum of the particle, not only is the travel distance small, but, in principle, only one particle at a time can be generated from the ultrasonic wave nozzle injection openings. Thus, only very small samples can be processed, so that this type of nozzle cannot be used in mass production. Moreover, in order to increase the travel distance, a separate air blowing means is needed, leading to a disadvantageous increase in the scale of the device.
Japanese Patent Application, First Publication No. Hei 4-21551 discloses a two-fluid nozzle capable of granulation on the order of tens of microns, the nozzle provided with a liquid injection opening; a ring-shaped vortex flow chamber formed at a position so that it surrounds the liquid injection opening; a plurality of revolving guide holes which extend in the form of a spiral to the vortex flow chamber and direct a high speed gas flow into the vortex flow chamber where a high speed revolving flow is generated; and a ring-shaped gas injection opening which sprays and forms a tapered conical high speed vortex flow which has a focal point in front of the liquid injection opening of the vortex flow chamber. However, this two-fluid nozzle for rendering gas into a high speed revolving flow also causes pressure damage when the liquid contains structures or components, such as vital cells, which are sensitive to pressure. Accordingly, nozzle of this type has a limited field of use.
Conventional examples of devices for freeze-drying a liquid containing a biological substance include a device which atomizes and then freeze-dries blood by using a gas to drip the liquid into liquid nitrogen. Such a method is disclosed in Research in Frozen Preservation of Erythrocytes by Droplet Freezing, Tomoyoshi Sato, Journal of the Hokkaido University School of Medicine, Vol. 58, No. 2, pages 144-153 (1983).
This device is formed of a duplex tube consisting of a polyethylene inner tube having an inner diameter of 0.4 mm and an outer tube which surrounds the inner tube and has an inner diameter of 3 mm. Blood is introduced via the inner tube and gas is introduced via the outer tube. A negative pressure is generated at the output end of the inner tube due to Bernoulli's principle, causing the blood to be introduced into the output end of the inner tube. The blood then drips from the inner tube into liquid nitrogen which has been positioned below. The particle size of the dripped blood is determined by the diameter of the inner tube, while the dripping speed is determined by the volume of the gas flowing through the outer tube.
However, conventional devices which atomize and freeze blood are simple negative pressure arrangements employing Bernoulli's principle. As a result, there is not sufficient control over the atomization. Moreover, the particle size is a large 0.7-2.8 mm, with the devices unable to form particles of 0.5 mm or less. It is difficult to maintain control when the particle size is 0.5 mm, so that the survival rate of erythrocytes and other blood cells is extremely poor (i.e., there is a high rate of hemolysis). Moreover, in order to dry the frozen blood, it is necessary to move the blood to a separate dryer. Accordingly, not only is the arrangement troublesome, but it becomes difficult to maintain the sterility of the frozen blood when moving it from the freezing to the drying device.